Our overall goal is to use E.coli as a model system to elucidate the basic mechanisms of protein localization that occur in all living cells. Our long-term objective is (i) to define and characterize the E.coli protein export machinery, (ii) to assign functions to its individual components, (iii) to understand how these functions are interelated to produce an efficient protein export pathway, and (iv) to determine how this pathway is regulated and coordinated with other essential cellular processes. At present, 9 putative export machinery components have been identified, but no specific biochemical function has been assigned to any of these components. The specific objective of these studies is to further define and elucidate the role of the secA gene product in catalyzing and regulating protein export in E.coli. Using a mutational analysis and a SecA-dependent in vitro protein translocation system, we will define the translocation activity(ies) catalyzed by SecA protein, determine which portions of the SecA polypeptide encodes this activity, and identify the export-related components that SecA protein interacts with in fulfilling this function. We will dissect the coregulation of secA with protein export proficiency further using a combination of mutational analysis and in vivo and in vitro assays to characterize which portions of the SecA polypeptide encodes its autogenous translational repressor activity, define the location and structure of the export-responsive translational operator, and elucidate the biochemical mechanism responsible for the coregulation observed. Since the mechanisms of protein localization are of central biological importance at all levels, from the functioning of individual protein molecules to the biogenesis and maintenance of normal and abnormal cell states, and since such mechanisms have been conserved throughout evolution, these studies with E.coli should be of broad significance.